Humidification chambers

ABSTRACT

A humidification chamber ( 10 ) for use in a breathing circuit to humidify gases before inhalation is disclosed. The humidification chamber ( 10 ) is adapted to contain a volume of liquid ( 20 ), and comprises a gas inlet port ( 16 ), a gas outlet port ( 16 ) and a fluid inlet ( 30 ) for introducing liquid into the humidification chamber ( 10 ). The fluid inlet ( 30 ) is provided with a filter member ( 60 ) including a plurality of exit apertures for enabling flow of liquid through the filter member ( 60 ). The filter member ( 60 ) also defines a collection chamber ( 69 ) that is disposed below the exit apertures, in use, such that foreign objects in the liquid that are unable to pass through the exit apertures fall under the influence of gravity into the collection chamber ( 69 ).

This invention relates to humidification chambers, and in particular tohumidification chambers for use in a breathing circuit to humidify gasesbefore inhalation.

The inhalation by patients of gases lacking sufficient moisture maydamage or irritate the respiratory tract, and/or desiccate essentialsecretions, especially in the case of patients whose upper airways havebeen bypassed. Gases within a breathing circuit are therefore usuallyhumidified before inhalation using a suitable humidification chamber.

Conventional humidification chambers generally contain a volume ofwater, and have two ports through which gases enter and exit thehumidification chamber, and means for heating the water. Furthermore,many humidification chambers include means for replacing water that islost from the humidification chamber so as to maintain the level of thewater relatively constant. Such means typically takes the form of afluid inlet including a valve for controlling the flow of liquid intothe chamber. The valve typically has a float actuator, whereby the riseand fall of the float actuator, in use, acts to open and close the valveso as to maintain the level of the water in the humidification chamberrelatively constant.

A problem associated with conventional humidification chambers, however,is that small foreign objects may be present in the liquid beingsupplied to the fluid inlet, which then enter the humidificationchamber. These small foreign objects may become entrained with therespiratory gases flowing through the humidification chamber, therebypotentially harming the patient. In addition, the small foreign objectsmay interfere with the functioning of the fluid inlet valve, forinstance by restricting movement of the float actuator and/or preventingthe formation of an effective seal between a valve seat and an actuatingmember of the valve.

There has now been devised an improved humidification chamber whichovercomes or substantially mitigates the above-mentioned and/or otherdisadvantages associated with the prior art.

According to a first aspect of the invention, there is provided ahumidification chamber for use in a breathing circuit to humidify gasesbefore inhalation, the humidification chamber being adapted to contain avolume of liquid, and comprising a gas inlet port, a gas outlet port anda fluid inlet for introducing liquid into the humidification chamber,wherein the fluid inlet is provided with a filter member including aplurality of exit apertures for enabling flow of liquid through thefilter member, and the filter member defines a collection chamber thatis disposed below the exit apertures, in use, such that foreign objectsin the liquid that are unable to pass through the exit apertures fallunder the influence of gravity into the collection chamber.

The humidification chamber according to the invention is advantageousprincipally because foreign objects within the liquid flowing throughthe fluid inlet that are too large to pass through the exit apertureswill fall under the influence of gravity into the collection chamber,and hence foreign objects that collect within the collection chamberwill not impede subsequent flow of liquid through the exit apertures.The present invention therefore reduces the risk of the fluid inletbecoming blocked, as well as reducing the risk of foreign objectsbecoming entrained with the respiratory gases flowing through thehumidification chamber or interfering with the functioning of a fluidinlet valve.

The filter member is preferably formed as a separate component from thefluid inlet, and is preferably fixed relative to the fluid inlet so thatthe filter member defines a partition within the fluid inlet throughwhich liquid flowing through the fluid inlet necessarily flows.

The filter member may be formed of any material that is suitable formedical applications, but the filter member is preferably formed ofinjection moulded plastics material. In presently preferred embodiments,the filter member is formed of a relatively rigid plastics material,such as a polycarbonate plastics material, so that the filter membermaintains its integrity and shape during normal use of thehumidification chamber.

The exit apertures are preferably sufficiently small in order to preventthe passage of a large proportion of the foreign bodies that might becontained within the liquid being supplied to the fluid inlet. However,the exit apertures are preferably also sufficiently large formanufacture of the filter member to be practicable. Furthermore, theexit apertures are preferably sufficiently large to enable an acceptablerate of flow through the fluid inlet during use. The exit aperturespreferably each have a length and/or width that is less than 1 mm, morepreferably less than 0.7 mm, and most preferably less than 0.5 mm. Inpresently preferred embodiments, each exit aperture has a width ofapproximately 0.26 mm and a length of approximately 0.36 mm. Thecollection chamber is preferably defined by a continuous wall of thefilter member, and hence does not include any exit apertures.

The filter member preferably comprises an inlet portion into whichliquid from a source of liquid flows, and an outlet portion in which theexit apertures and the collection chamber are formed. The outlet portionpreferably has the form of a liquid conduit having exit apertures withinits side wall, and a collection chamber is preferably defined by aclosed end of the outlet portion. The outlet portion is preferablydisposed generally vertically, and the collection chamber is preferablyformed at the lowermost end of the outlet portion. The outlet portion ispreferably of tubular structure, and is most preferably generallycylindrical. In this arrangement, the outlet portion of the filtermember preferably extends along a central, longitudinal axis of thefluid inlet, and is preferably separated from the interior surface ofthe fluid inlet at all points.

A wall of the filter member preferably comprises a plurality of elongateopenings, and a plurality of generally orthogonal ribs that are formedon a surface of that wall and extend across those openings, so as todefine an array of exit apertures. Where the outlet portion is oftubular structure, the exit apertures are preferably formed in a sidewall of the outlet portion. In this case, the orthogonal ribs arepreferably formed on the interior surface of the outlet portion.Furthermore, the elongate openings preferably extend alongcircumferences of the outlet portion, and the orthogonal ribs arepreferably orientated longitudinally along the outlet portion.

The filter member preferably includes an inlet portion that is fixed tothe fluid inlet, and is most preferably fixed to an interior surface ofthe fluid inlet, so that liquid supplied to the fluid inlet necessarilyflows through the filter member. Where the fluid inlet has substantiallyconstant cross-sectional dimensions, the outlet portion of the filtermember preferably has reduced cross-sectional dimensions relative to theinlet portion so that the outlet portion is separated from the interiorsurface of the fluid inlet. In presently preferred embodiments, theinlet and outlet portions of the filter member are both cylindrical, andhave substantially co-extensive central axes. In addition, the outletportion preferably extends a short distance into the interior of theinlet portion, so that a secondary collection chamber is defined aboutthe entrance to the outlet portion.

The humidification chamber preferably includes a valve for controllingthe level of liquid within the humidification chamber. In particular,the fluid inlet preferably includes a primary valve seat, and the valvepreferably comprises an actuating member that is movable in response toa change in the level of liquid within the humidification chamberbetween an open configuration in which the actuating member isdisengaged from the primary valve seat such that liquid is able to flowthrough the fluid inlet into the humidification chamber when the liquidwithin the humidification chamber is below a predetermined acceptablelevel, and a closed configuration in which the actuating member isengaged with the primary valve seat such that liquid is prevented fromflowing through the fluid inlet into the humidification chamber when theliquid within the humidification chamber is at or above thepredetermined acceptable level.

In the event that very small foreign objects pass through the exitopenings and enter the humidification chamber, these foreign objects mayreduce the effectiveness of the seal formed between the actuating memberand the primary valve seat so that the valve fails to prevent flow ofliquid through the fluid inlet into the humidification chamber. Thefluid inlet preferably therefore includes a secondary valve seat, andthe actuating member is preferably deformable in response to an increasein the level of liquid within the humidification chamber above thepredetermined acceptable level to a deformed configuration in which theactuating member engages the secondary valve seat such that liquid isprevented from flowing through the fluid inlet into the humidificationchamber.

Hence, according to a further aspect of the invention, there is provideda humidification chamber for use in a breathing circuit to humidifygases before inhalation, the humidification chamber being adapted tocontain a volume of liquid, and comprising a gas inlet port, a gasoutlet port, a fluid inlet including a primary valve seat, and a valvehaving an actuating member that is movable in response to a change inthe level of liquid within the humidification chamber between an openconfiguration in which the actuating member is disengaged from theprimary valve seat such that liquid is able to flow through the fluidinlet into the humidification chamber when the liquid within thehumidification chamber is below a predetermined acceptable level, and aclosed configuration in which the actuating member is engaged with theprimary valve seat such that liquid is prevented from flowing throughthe fluid inlet into the humidification chamber when the liquid withinthe humidification chamber is at or above the predetermined acceptablelevel, wherein the fluid inlet includes a secondary valve seat, and theactuating member is deformable in response to an increase in the levelof liquid within the humidification chamber above the predeterminedacceptable level to a deformed configuration in which the actuatingmember engages the secondary valve seat such that liquid is preventedfrom flowing through the fluid inlet into the humidification chamber.

The humidification chamber according to this aspect of the invention isadvantageous principally because, in the event that the effectiveness ofthe seal formed between the actuating member and the primary valve seatis impaired so that the valve fails to prevent flow of liquid throughthe fluid inlet into the humidification chamber, the actuating memberwill be deformed by the rising liquid level within the humidificationchamber into engagement with the secondary valve seat so as to preventthe flow of liquid through the fluid inlet.

The actuating member is preferably operably linked to a float so as tobe movable in response to movement of the float. The force that causesthe actuating member to deform into engagement with the secondary valveseat is preferably generated by the buoyancy of the float, whichpreferably increases as the level of liquid within the humidificationchamber increases.

The primary and secondary valve seats are both preferably continuous,and the primary valve seat is preferably disposed within the space thatis bordered by the secondary valve seat. In presently preferredembodiments the primary and secondary valve seats are substantiallycircular in shape, and are preferably disposed in a generally concentricarrangement. Furthermore, the valve is preferably arranged such that theactuating member engages only the primary valve seat in the closedconfiguration, and the actuating member engages both the primary valveseat and the secondary valve seat in the deformed configuration. Mostpreferably, the actuating member includes an operative surface thatengages the valve seats, in use. This operative surface is preferablysubstantially flat in the open configuration. The secondary valve seatis preferably therefore disposed a greater distance from the operativesurface of the actuating member, relative to the primary valve seat, inthe open configuration.

The actuating member may be defined by part of the float. However, inpresently preferred embodiments, the actuating member is a separatecomponent from the float. The actuating member is preferably flexible inform, and is preferably formed of a resilient material, such as athermoplastic elastomer, in order to form a reliable and effective sealwith the valve seats.

In presently preferred embodiments, the actuating member has the form ofa valve cushion that is engaged with the float, and at least part of thevalve cushion is preferably separated from the exterior surface of thefloat so as to allow deformation of the valve cushion, in use, towardsthe exterior surface of the float. For instance, the valve cushion mayhave the form of a cup that is mounted within a recess in an uppersurface of the float. In this case, a base of the valve cushionpreferably defines the operative surface, and is preferably separatedfrom the base of the recess in order to allow deformation of the valvecushion during use.

The fluid inlet preferably extends through an opening in a wall of thehumidification chamber. The fluid inlet is preferably adapted at one endfor connection to a source of liquid, and at the other end forintroducing liquid into the humidification chamber. Most preferably, thefluid inlet includes an exit orifice through which liquid may enter thehumidification chamber, and the valve seats preferably extend about thisexit orifice. The exit orifice is preferably of reduced diameterrelative to the remainder of the fluid inlet, and the fluid inletpreferably includes a tapered end portion that leads to the exitorifice. The primary and secondary valve seats are preferably formedintegrally with the fluid inlet, and preferably have narrow operativesurfaces.

The float is preferably slidably mounted relative to the fluid inlet.Most preferably, the float is slidably mounted relative to a guidesleeve. The guide sleeve preferably extends from an interior surface ofthe humidification chamber, and the fluid inlet is preferably disposedwithin the guide sleeve. In presently preferred embodiments, at leastpart of the float is slidably mounted within guide sleeve, and the guidesleeve preferably includes longitudinal ribs on its interior surfacethat define channels along which liquid may flow down the exteriorsurface of the float.

The liquid is normally water, or a suitable aqueous solution. Duringuse, the level of liquid within the humidification chamber willgradually reduce as the gases flowing through the humidification chamberare humidified. Most preferably, the valve is adapted to maintain thelevel of liquid within the humidification chamber within a relativelynarrow range about the predetermined acceptable level.

The humidification chamber preferably comprises an upper portion that isformed of plastic material, most preferably by injection moulding, and abase formed of a good heat conductor, such as a suitable metal, thattogether define an enclosure for containing the liquid. The base ispreferably generally circular in shape, and the upper portion preferablyhas a generally cylindrical side wall. The gas inlet port and gas outletport are preferably formed in an upper wall of the humidificationchamber, and preferably comprise upstanding tubular connectors that areadapted for connection to conventional respiratory connectors andtubing. The fluid inlet and the guide sleeve are preferably formedintegrally with the upper portion of the humidification chamber, and arepreferably situated generally centrally in an upper wall of thehumidification chamber.

Preferred embodiments of the invention will now be described in greaterdetail, by way of illustration only, with reference to the accompanyingdrawings, in which

FIG. 1 is a first cross-sectional view of a humidification chamberaccording to the invention, in which a primary float is acting tomaintain a fluid inlet valve in a closed configuration;

FIG. 2 is a second cross-sectional view of the humidification chamber,in which a secondary float is acting to maintain a fluid inlet valve ina closed configuration;

FIG. 3 is a cross-sectional view of the primary float;

FIG. 4 is a cross-sectional view of the secondary float;

FIG. 5 is a fragmentary cross-sectional view of a fluid inlet valve ofthe humidification chamber;

FIG. 6 is a perspective view of a fluid inlet filter of thehumidification chamber;

FIG. 7 is a side view of the fluid inlet filter; and

FIG. 8 is a cross-sectional view, along the line VIII-VIII in FIG. 7, ofthe fluid inlet filter.

FIGS. 1 and 2 show a humidification chamber according to the invention,which is generally designated 10. The humidification chamber 10comprises a body 12 that is injection moulded in a transparent plasticsmaterial, and a metal base 14 fixed to an open lower end of the body 12.The body 12 and the base 14 of the humidification chamber 10 cooperateto define an enclosure for containing, in use, a volume of water 20.

The body 12 of the humidification chamber 10 comprises a generallycylindrical, but slightly tapered, side wall that is fixed at its lowerend to the periphery of the base 14, and an upper wall that has thegeneral shape of a shallow dome. The base 14 of the humidificationchamber 10 has the form of a circular disc, with an upturned rim that issealed to a flange at the lower end of the side wall of the body 12.

Two inlet/outlet ports 16 that have the form of 22 mm tubular connectorsextend upwardly from openings in the upper wall of the humidificationchamber 10. Each inlet/outlet port 16 also includes a hemi-cylindricalextension 17 and a circular end baffle 18 within the enclosure of thehumidification chamber 10, which together define a lower opening thatfaces the side wall of the humidification chamber 10. In addition, thehumidification chamber 10 includes four baffles 19 (two of which arevisible in FIG. 1) that are each formed integrally with the body 12 ofthe humidification chamber 10, and each extend downwardly from theinterior surface of the upper wall. Each baffle 19 is arcuate in itshorizontal dimension, and extends horizontally between an interiorsurface of the side wall of the humidification chamber 10 and a positionadjacent to, but separated from, the guide sleeve 32.

Referring now also to FIG. 5, the humidification chamber 10 alsocomprises a fluid inlet 30 that extends through an opening in the centreof the upper wall of the humidification chamber 10. The fluid inlet 30comprises an upper cylindrical portion with an open upper end, anintermediate cylindrical portion of reduced diameter, and a taperedlower end portion that terminates within the humidification chamber 10with a lower opening of significantly reduced diameter relative to theopen upper end.

As shown most clearly in FIG. 5, the exterior surface of the fluid inlet30 that surrounds the lower opening comprises two concentricprojections, the inner projection being of greater extent than the outerprojection. These concentric projections each terminate with arelatively narrow edge, and these relatively narrow edges define aninner valve seat 34 and an outer valve seat 35, which are both adaptedto form a seal with an elastomeric valve cushion 42 that is described inmore detail below.

A filter 60 is fixed within the fluid inlet 30 so that water flowingthrough the fluid inlet 30 necessarily flows through the filter 60. Thefilter 60 is shown most clearly in FIGS. 6, 7 and 8, and comprises acylindrical inlet portion 62, and a cylindrical outlet portion 64 ofreduced diameter. The inlet portion 62 has an open end, and an end fromwhich the outlet portion 64 projects. The outlet portion 64 has an openend situated a short distance within the inlet portion 62, so as todefine an annular, first collection chamber 68 of the filter 60, and theoutlet portion 64 extends through the end wall of the inlet portion 62.The projecting part of the outlet portion 64 has a closed end and a sidewall that includes six elongate openings 65, which each reduce graduallyin width before leading into the interior of the outlet portion 64. Theopenings 65 are arranged in three circumferentially-extending pairs atequally spaced positions along the longitudinal axis of the outletportion 64. Furthermore, longitudinal members 66 that extendperpendicularly across the openings 65 are formed on the interiorsurface of the outlet portion 64, so that an array of apertures isdefined in the side wall of the outlet portion 64. An end portion of theoutlet portion 64 does not include any apertures, and hence defines asecond collection chamber 69 of the filter 60. In this embodiment, thefilter 60 is injection moulded in polycarbonate plastics material, andeach aperture has a width of approximately 0.26 mm and a length ofapproximately 0.36 mm.

The inlet portion 62 of the filter 60 is received with an interferencefit within the upper portion of the fluid inlet 30, and is fixed usingsuitable adhesive so that there is a seal between the external surfaceof the inlet portion 62 of the filter 60 and the interior surface of theupper portion of the fluid inlet 30. The outlet portion 64 of the filter60 is sized so that its exterior surface is separated, at all points,from the interior surface of the intermediate portion and tapered lowerend portion of the fluid inlet 30. The inlet portion 62 of the filter 60is also appropriately sized so as to receive a connector of a suitableliquid conduit, such that the fluid inlet 30 communicates with a sourceof water during use.

As shown in FIGS. 1 and 2, the upper wall of the humidification chamber10 includes a centrally positioned and downwardly extending guide sleeve32 of cylindrical shape, which is of greater diameter than the fluidinlet 30 and extends co-axially therewith. Eight longitudinal ribs 33are provided on the interior surface of the guide sleeve 32 atequiangularly spaced positions, so as to form channels for the water 20being supplied through the fluid inlet 30 to flow down the exteriorsurface of the primary float 40 during use.

A fluid inlet valve controls the flow of water 20 through the fluidinlet 30. The fluid inlet valve comprises a primary float 40, a valvecushion 42, and a secondary float 50. The primary float 40 is shown inisolation in FIG. 3, and comprises an upper portion and a lower portion,which are integrally formed in a plastics material using an injectionmoulding process that is described in published European patentapplication EP 1366881.

The upper portion of the primary float 40 is a generally cylindricaltube with relatively thin walls and a diameter that increases graduallyand slightly from an open upper end to a open lower end. The exteriorsurface of the upper portion is highly polished to enable a low-frictionslidable engagement with the guide sleeve 32, and includes a pair ofcircumferentially extending, and diametrically opposed, projections 48.These projections 48 are adapted to be engaged by the secondary float50, as discussed in more detail below, and each comprises an operativelower surface that is orientated perpendicularly to the adjacent surfaceof the upper portion of the primary float 40.

A circular partition 44 extends across the interior of the upper portionof the primary float 40 so as to define a cylindrical recess in theupper surface of the primary float 40. In addition, the upper portionincludes four openings 46, at equiangularly spaced positions, in a lowerpart of its wall below the circular partition 44.

The lower portion of the primary float 40 is also generally cylindricalin form, but has walls of greater thickness than those of the upperportion of the float 40. The plastics material of the lower portion hasa foam-like structure with many pockets of gas trapped within theplastics material. The primary float 40 is located within the enclosureof the humidification chamber 10 such that the lower end of the primaryfloat 40 rests on the base 14 of the humidification chamber 10 until asufficient volume of water 20 is introduced into the humidificationchamber 10, and the majority of the upper portion of the primary float40 is received with a slidable fit within the guiding sleeve 46.

A valve cushion 42, which is formed of elastomeric material, has theform of a cup and is received with an interference fit within thecylindrical recess in the upper surface of the primary float 40. Theopen upper end of the valve cushion 42 has an outwardly extending flangethat rests upon the rim of the upper portion of the primary float 40,and the base of the valve cushion 42 is separated from the circularpartition 44 of the primary float 40 so as to allow deformation of thevalve cushion 42 towards the central partition 44 during use.

The secondary float 50 is shown in isolation in FIG. 4, and comprisesupper and lower members 52,54 that are injection moulded as a singlecomponent, and joined by a hinge 53. The upper and lower members 52,54together define an internal chamber that provides the secondary float 50with approximately four times the buoyancy of the primary float 40.However, as shown in FIG. 2, a vent 55 is provided in the upper wall ofthe secondary float 50 to prevent the build-up of excessive pressurewithin the secondary float 50 during use.

The upper member 52 defines a side wall and an upper wall of thesecondary float 50, and the lower member 54 defines an cylindrical innerwall and a base of the secondary float 50. The inner edge of the uppermember 52, and the upper edge of the lower member 54, are formed withcorresponding annular projections with enlarged heads that engage eachother with a snap fit. Similarly, the outer edges of the upper and lowermembers 52,54 are formed with corresponding annular projections withenlarged heads that engage each other with a snap fit. In this way, theupper and lower members 52,54, joined by the hinge 53, are injectionmoulded as a single component, and the upper and lower members 52,54 arethen rotated into engagement with each other, with a snap fit, so as toform the secondary float 50. The snap fit between correspondingprojections is adapted to prevent the ingress of water into the internalchamber of the secondary float 50 during use. If necessary, however, theupper and lower members 52,54 are also glued together.

The upper member 52 of the secondary float 50 has a shape that conformsgenerally to the interior surface of the upper wall of thehumidification chamber 10, such that the secondary float 50 is adaptedto lie alongside the upper wall of the humidification chamber 10. Inparticular, the upper member 52 has a generally cylindrical, butslightly tapered, side wall and an annular upper wall, as shown mostclearly in FIGS. 1 and 4. In addition, the upper member 52 comprisesshallow depressions for accommodating the extensions 17 and baffles 18of the inlet/outlet ports 16, as shown most clearly in FIG. 2, and moreextensive recesses for accommodating the arcuate baffles 19 dependingfrom the upper wall of the humidification chamber 10.

The lower member 54 comprises an annular base that is shaped so as toaccommodate an upper part of the lower portion of the primary float 40,and a cylindrical inner portion that is adapted for slidable engagementwith the exterior surface of the guide sleeve 32. The cylindrical innerportion has open upper and lower ends, and six longitudinal ribs 56formed on its inner surface at equiangularly spaced positions. Inaddition, an annular flange 58 extends inwardly from the lower end ofthe inner portion of the secondary float 50, and includes an operativeupper surface adapted to engage the projections 48 on the exteriorsurface of the primary float 40. The flange 58 also includes a series ofopenings 57 for enabling the throughflow of water 20 during use.

The lower member 54 also includes three legs 59 that rest upon the base14 of the humidification chamber 10, and hence maintain the secondaryfloat 50 at a minimum height, during normal operation. As shown in FIG.2, the legs 59 each include an internal chamber that is in communicationwith the remainder of the interior of the secondary float 50.

Finally, the humidification chamber 10 includes a liquid level indicator70 that enables a user to readily ascertain the level of the water 20.This liquid level indicator comprises an annular float 70 and suitablelevel indication marks (not visible in FIGS. 1 and 2), and is describedin published European patent application EP 1347797.

The humidification chamber 10 is connected to a breathing circuit byattaching a gas inlet conduit (not shown in the Figures) to one of theinlet/outlet ports 16, and attaching a gas outlet conduit to the otherinlet/outlet port 16. A heat source (not shown in the Figures) is placedin contact with the base 14 of the humidification chamber 10, so as toheat the water 20 within the humidification chamber 10 to a desiredtemperature.

A liquid conduit (not shown in the Figures) is then connected at one endto a source of water, and at the other end to the fluid inlet 30, sothat water 20 is continuously supplied to the filter 60 and fluid inlet30. When the source of water 20 is first connected to the humidificationchamber 10, water 20 flows through the filter 60 and fluid inlet 30,fills the valve cushion 42, and then flows through the channels definedby the longitudinal ribs 33 of the guiding sleeve 32, through theopenings 57 in the flange 58 of the secondary float 50, and down theexterior surface of the primary float 40 onto the base 14 of thehumidification chamber 10. The humidification chamber 10 thereforebegins to fill with water 20.

The source of water may be a flexible bag that is charged with water, orsome other kind of water reservoir. Such sources often contain foreignobjects, which may be present as a result of the manufacture, storageand/or previous use of the bag or reservoir. However, the filter 60 actsto prevent the passage of foreign objects through the fluid inlet 30into the enclosure of the humidification chamber 10. In use, foreignobjects collect, under the influence of gravity, in either the firstcollection chamber 68 in the inlet portion 62 of the filter 60, or thesecond collection chamber 69 in the outlet portion 64 of the filter 60.In each case, the collected foreign objects within the first and secondcollection chambers 68,69 are far removed from the open upper end of theoutlet portion 64 and the apertures in the side wall of the outletportion 64, and hence will not impede the flow of water through thefilter 60 or interfere with normal operation of the valve mechanism.

When the water 20 within the humidification chamber 10 reaches a certainlevel, the primary float 40 is raised relative to the remainder of thehumidification chamber 10 by its buoyancy. The primary float 40 is heldin an upright position by the guiding sleeve 32. The primary float 40will continue to rise until the water 20 reaches a sufficient level forthe valve cushion 42 to be urged against the inner valve seat 34 of thefluid inlet 30 with enough force to form an effective seal, and henceprevent the inflow of water 20 through the lower opening of the fluidinlet 30. This configuration is shown in FIG. 1.

There will generally be some deformation of the valve cushion 42 towardsthe central partition 44 of the primary float 40 before an effectiveseal is formed between the valve cushion 42 and the inner valve seat 34,so that the inflow of water 20 into the humidification chamber 10ceases. In the event that an effective seal is not formed between thevalve cushion 42 and the inner valve seat 34, for instance due to thepresence of foreign bodies on the operative surfaces of the valvecushion 42 and/or the inner valve seat 34, the primary float 40 willcontinue to rise and deformation of the valve cushion 42 will increaseuntil the valve cushion 42 is urged against the outer valve seat 35 ofthe fluid inlet 30 with enough force to form an effective seal, andhence prevent the inflow of water 20 through the lower opening of thefluid inlet 30.

In use, gases intended for inhalation by a patient are supplied to thegas inlet conduit under positive pressure. The pressure differentialcreated between the gas inlet conduit and the gas outlet conduit causesgases to flow from the gas inlet conduit, through the enclosure of thehumidification chamber 10, to the gas outlet conduit. This causes watervapour within the chamber 10 to be entrained in the flow of gas throughthe humidification chamber 10, so that the gas within the gas outletconduit has an increased humidity relative to the gas within the gasinlet conduit.

As water is entrained in the flow of gas through the humidificationchamber 10, the level of the water 20 in the humidification chamber 10will gradually reduce. The primary float 40 will therefore be loweredrelative to the remainder of the humidification chamber 10. This willcontinue until the valve cushion 42 of the fluid inlet valve becomesseparated from the lower opening of the fluid inlet 30, such that water20 is allowed to flow into the humidification chamber 10 through thefluid inlet 30. As the level of water 20 increases once again, theprimary float 40 will rise relative to the remainder of thehumidification chamber 10. The primary float 40 will continue to riseuntil the water 20 reaches a sufficient level for the valve cushion 42to be once again urged against the inner and/or outer valve seat 34,35of the lower opening of the fluid inlet 30 with enough force to form aneffective seal, and hence prevent the inflow of water 20 through thelower opening. In this way, the level of the water 20 is maintainedrelatively constant during use. In addition, the openings in the primaryfloat 40 prevent the buoyancy of the primary float 40 being affected byair becoming trapped between the surface of the water 20 and theinterior surface of the lower portion of the primary float 40.

In the event that the fluid inlet valve becomes damaged, for instance bysmall foreign objects limiting movement of the primary float 40 and/ordamage to the primary float 40 reducing its buoyancy, the level of water20 within the humidification chamber 10 will rise beyond the level atwhich the fluid inlet valve closes during normal operation. However,when the water 20 within the humidification chamber 10 reaches a certainlevel, the secondary float 50 is raised relative to the remainder of thehumidification chamber 10 by its buoyancy, and held in an uprightposition by the guiding sleeve 32.

The secondary float 50 will continue to rise until the water 20 reachesa sufficient level for the flange 58 of the secondary float 50 toimpinge upon, and hence engage, the projections 48 of the primary float40. As the level of water 20 within the humidification chamber 10increases, the upward buoyancy force imparted upon the secondary float50, and hence the upward force imparted by the secondary float 50 uponthe primary float 40, will increase until the primary float 40 is raisedrelative to the remainder of the humidification chamber 10. Since thesecondary float 50 has a buoyancy that is approximately four times thebuoyancy of the primary float 40, the upward force imparted by thesecondary float 50 upon the primary float 40 will overcome common damageto the fluid inlet valve, such as limitation in the movement of theprimary float 40 and/or damage to the primary float 40 reducing itsbuoyancy. The upward force imparted by the secondary float 50 upon theprimary float 40 will cause the primary float 40 to be raised relativeto the remainder of the humidification chamber 10 until the valvecushion 42 is urged against the inner valve seat 34 and/or the outervalve seat 35 of the fluid inlet 30 with enough force to form aneffective seal, and hence prevent the inflow of water 20 through thelower opening of the fluid inlet 30, as discussed in detail above. Thisconfiguration is shown in FIG. 2.

1. A humidification chamber for use in a breathing circuit to humidifygases before inhalation, the humidification chamber being adapted tocontain a volume of liquid, and comprising a gas inlet port, a gasoutlet port and a fluid inlet for introducing liquid into thehumidification chamber, wherein the fluid inlet is provided with afilter member including a plurality of exit apertures for enabling flowof liquid through the filter member, and the filter member defines acollection chamber that is disposed below the exit apertures, in use,such that foreign objects in the liquid that are unable to pass throughthe exit apertures fall under the influence of gravity into thecollection chamber.
 2. A humidification chamber as claimed in claim 1,wherein the filter member is formed as a separate component from thefluid inlet.
 3. A humidification chamber as claimed in claim 2, whereinthe filter member is fixed relative to the fluid inlet so that thefilter member defines a partition within the fluid inlet through whichliquid flowing through the fluid inlet necessarily flows.
 4. Ahumidification chamber as claimed in claim 1, wherein the filter memberis formed of a relatively rigid plastics material, so that the filtermember maintains its integrity and shape during normal use of thehumidification chamber.
 5. A humidification chamber as claimed in claim1, wherein the exit apertures each have a length and/or width that isless than 1 mm.
 6. A humidification chamber as claimed in claim 1,wherein the exit apertures each have a length and/or width that is lessthan 0.7 mm.
 7. A humidification chamber as claimed in claim 1, whereinthe exit apertures each have a length and/or width that is less than 0.5mm.
 8. A humidification chamber as claimed in claim 1, wherein thecollection chamber is defined by a continuous wall of the filter member,and hence does not include any exit apertures.
 9. A humidificationchamber as claimed in claim 1, wherein the filter member comprises aninlet portion into which liquid from a source of liquid flows, and anoutlet portion in which the exit apertures and the collection chamberare formed.
 10. A humidification chamber as claimed in claim 9, whereinthe outlet portion has the form of a liquid conduit having exitapertures within its side wall, and the collection chamber is defined bya closed end of the outlet portion.
 11. A humidification chamber asclaimed in claim 9, wherein the outlet portion is disposed generallyvertically, and the collection chamber is formed at the lowermost end ofthe outlet portion.
 12. A humidification chamber as claimed in claim 9,wherein the outlet portion is of tubular structure.
 13. A humidificationchamber as claimed in claim 9, wherein the outlet portion of the filtermember extends along a central, longitudinal axis of the fluid inlet,and is separated from the interior surface of the fluid inlet at allpoints.
 14. A humidification chamber as claimed in claim 9, wherein awall of the filter member comprises a plurality of elongate openings,and a plurality of generally orthogonal ribs that are formed on asurface of that wall and extend across those openings, so as to definean array of exit apertures.
 15. A humidification chamber as claimed inclaim 14, wherein the outlet portion is of tubular structure, and theexit apertures are formed in a side wall of the outlet portion.
 16. Ahumidification chamber as claimed in claim 14, wherein the orthogonalribs are formed on the interior surface of the outlet portion.
 17. Ahumidification chamber as claimed in claim 14, wherein the elongateopenings extend along circumferences of the outlet portion, and theorthogonal ribs are orientated longitudinally along the outlet portion.18. A humidification chamber as claimed in claim 9, wherein the inletportion of the filter member is fixed to the fluid inlet, so that liquidsupplied to the fluid inlet necessarily flows through the filter member.19. A humidification chamber as claimed in claim 9, wherein the outletportion of the filter member has reduced cross-sectional dimensionsrelative to the inlet portion, so that the outlet portion is separatedfrom the interior surface of the fluid inlet.
 20. A humidificationchamber as claimed in claim 9, wherein the inlet and outlet portions ofthe filter member are both cylindrical, and have substantiallyco-extensive central axes.
 21. A humidification chamber as claimed inclaim 20, wherein the outlet portion extends a short distance into theinterior of the inlet portion, so that a secondary collection chamber isdefined about the entrance to the outlet portion.
 22. A humidificationchamber as claimed in claim 1, wherein the humidification chamberincludes a valve for controlling the level of liquid within thehumidification chamber.
 23. A humidification chamber as claimed in claim22, wherein the fluid inlet includes a primary valve seat, and the valvecomprises an actuating member that is movable in response to a change inthe level of liquid within the humidification chamber between an openconfiguration in which the actuating member is disengaged from theprimary valve seat such that liquid is able to flow through the fluidinlet into the humidification chamber when the liquid within thehumidification chamber is below a predetermined acceptable level, and aclosed configuration in which the actuating member is engaged with theprimary valve seat such that liquid is prevented from flowing throughthe fluid inlet into the humidification chamber when the liquid withinthe humidification chamber is at or above the predetermined acceptablelevel.
 24. A humidification chamber as claimed in claim 23, wherein thefluid inlet includes a secondary valve seat, and the actuating member isdeformable in response to an increase in the level of liquid within thehumidification chamber above the predetermined acceptable level to adeformed configuration in which the actuating member engages thesecondary valve seat such that liquid is prevented from flowing throughthe fluid inlet into the humidification chamber.
 25. A humidificationchamber for use in a breathing circuit to humidify gases beforeinhalation, the humidification chamber being adapted to contain a volumeof liquid, and comprising a gas inlet port, a gas outlet port, a fluidinlet including a primary valve seat, and a valve having an actuatingmember that is movable in response to a change in the level of liquidwithin the humidification chamber between an open configuration in whichthe actuating member is disengaged from the primary valve seat such thatliquid is able to flow through the fluid inlet into the humidificationchamber when the liquid within the humidification chamber is below apredetermined acceptable level, and a closed configuration in which theactuating member is engaged with the primary valve seat such that liquidis prevented from flowing through the fluid inlet into thehumidification chamber when the liquid within the humidification chamberis at or above the predetermined acceptable level, wherein the fluidinlet includes a secondary valve seat, and the actuating member isdeformable in response to an increase in the level of liquid within thehumidification chamber above the predetermined acceptable level to adeformed configuration in which the actuating member engages thesecondary valve seat such that liquid is prevented from flowing throughthe fluid inlet into the humidification chamber.
 26. A humidificationchamber as claimed in claim 25, wherein the actuating member is operablylinked to a float so as to be movable in response to movement of thefloat.
 27. A humidification chamber as claimed in claim 26, wherein theforce that causes the actuating member to deform into engagement withthe secondary valve seat is generated by the buoyancy of the float,which increases as the level of liquid within the humidification chamberincreases.
 28. A humidification chamber as claimed in claim 25, whereinthe primary and secondary valve seats are both continuous.
 29. Ahumidification chamber as claimed in claim 28, wherein the primary valveseat is disposed within the space that is bordered by the secondaryvalve seat.
 30. A humidification chamber as claimed in claim 25, whereinthe primary and secondary valve seats are substantially circular inshape.
 31. A humidification chamber as claimed in claim 30, wherein theprimary and secondary valve seats are disposed in a generally concentricarrangement.
 32. A humidification chamber as claimed in claim 25,wherein the valve is arranged such that the actuating member engagesonly the primary valve seat in the closed configuration, and theactuating member engages both the primary valve seat and the secondaryvalve seat in the deformed configuration.
 33. A humidification chamberas claimed in claim 25, wherein the actuating member includes anoperative surface that engages the valve seats, in use, and theoperative surface is substantially flat in the open configuration, suchthat the secondary valve seat is disposed a greater distance from theoperative surface of the actuating member, relative to the primary valveseat, in the open configuration.
 34. A humidification chamber as claimedin claim 25, wherein the actuating member has the form of a valvecushion that is engaged with the float, and at least part of the valvecushion is separated from the exterior surface of the float so as toallow deformation of the valve cushion, in use, towards the exteriorsurface of the float.
 35. A humidification chamber as claimed in claim34, wherein the valve cushion has the form of a cup that is mountedwithin a recess in an upper surface of the float, and a base of thevalve cushion defines the operative surface and is separated from thebase of the recess in order to allow deformation of the valve cushionduring use.
 36. A humidification chamber as claimed in claim 25, whereinthe fluid inlet extends through an opening in a wall of thehumidification chamber, and the fluid inlet is adapted at one end forconnection to a source of liquid, and at the other end for introducingliquid into the humidification chamber.
 37. A humidification chamber asclaimed in claim 36, wherein the fluid inlet includes an exit orificethrough which liquid may enter the humidification chamber, and the valveseats extend about this exit orifice.
 38. A humidification chamber asclaimed in claim 37, wherein the exit orifice is of reduced diameterrelative to the remainder of the fluid inlet.
 39. A humidificationchamber as claimed in claim 38, wherein the fluid inlet includes atapered end portion that leads to the exit orifice.
 40. A humidificationchamber as claimed in claim 25, wherein the primary and secondary valveseats are formed integrally with the fluid inlet.